The setting of gain of an audio channel and of the mixing of multiple channels prior to recording is an extremely important function in the recording of music and sounds and speech, particularly in the television industry where video cameramen with recorders commonly go to the scene of a newsworthy event and record visually and in audio form the event, often working under extreme conditions. The cameraman may be his own audio man as well and his full attention, particularly visually, is concentrated upon the video camera, where he can not look at a common vu-meter.
In the case where a scene is recorded simultaneously in video and audio, any distortion in the audio channel greatly diminishes the acceptability of the recording produced. Once recorded, the distortion is virtually impossible to eliminate. Attempts made after the fact to correct distortion have met with little success. Another approach is merely to maintain gain at such a level to insure freedom from distortion, however, this often results in reduction or loss of good audio signal, due to high noise levels. Since the signal should be amplified above the noise level as high as possible without overloading any part of the recording channel which would result in distortion.
Other types of mixing circuits have employed automatic gain control, but I have found that automatic gain control does not provide a maximum usable undistorted good signal above noise level.
Predistortion circuits have been used in a number of applications usually in the signal channel e.g. Dolby Systems, however, not in a branch control channel.